1. Technical Field of the Invention
This invention relates to an aggregate and method for making the same which utilizes coal ash slag from coal gasification systems. More particularly, the present invention relates to a lightweight aggregate having a lesser density than the coal ash slag from which it was formed allowing for its use as a structural material. Further, the processed aggregate includes interlaced channels of characteristic diameter and length which allow for its use in chemical filtering or reaction processes.
2. Description of the Prior Art
Several coal gasification systems have been developed over the past decade. These entrained coal gasification systems feature the partial combustion of coal using an oxidant resulting in the production of synthesis gas (syngas). To date, such systems have not generally been commercially attractive, because they have typically had higher operating costs than other existing conventional processes.
Specifically, in these processes all or substantially all of the carbon found in the coal is reacted at an elevated temperature and at an elevated pressure to form the desired syngas. Systems vary with respect to methods for feeding the coal; i.e., coal-water slurry systems and dry feed systems. In these systems the reaction temperature is above the melting point of the ash present in the coal fed to the system. Therefore, the ash is molten to allow the oxidant to react with the carboneous material.
When the desired reaction has occurred, typically, the flowing stream of gases and molten ash is rapidly cooled by quenching in a liquid pool of water. The slag produced by standard coal gasification systems has been shown to be relatively dense, impervious to leaching and relatively inert. The slag material is continuously removed from the system by equipment that permits an intermittent or continuous let down of the slag-water by-product from the elevated pressure of the particular system. Once removed, the slag must be disposed of in a safe and suitable manner. This step further adds to the total cost of producing syngas.
Historically, utilization of solid waste materials from. chemical processing of feedstocks has received limited attention. Recently, somewhat greater effort is being made to utilize coal combustion waste products (fly ash) due to the increasing costs of disposal and the limited availability of land for this purpose, particularly in areas of high population density. At present, coal combustion waste materials are utilized to a far greater degree in Europe than in the U.S.
There are a number of methods for utilizing waste ash material produced from coal-burning industrial power plants. Illustrative of such methods is U.S. Pat. No. 2,576,565, issued Nov. 27, 1951 to Brown, which discloses a ceramic product and method of making the same which utilizes coal ash from coal burning power plants collected from stack gases and slag produced from the cooled molten coal ash. The ash used in this process possesses properties at least equivalent to conventional clay or shale useful for producing a ceramic product. Therefore, once the ash has been screened to the desired size, it may be used directly as a raw material for the ceramic product.
Further patents illustrative of methods of producing ceramic products using coal ash resulting from coal burning plants are U.S. Pat. Nos. 1,580,906 issued Apr. 13, 1926 to Korber; 2,055,706 issued Sep. 29, 1936 to Ramseyer; and 2,247,120 issued Jun. 24, 1941 to Fitzgerald.
Another example of utilizing coal ash produced by coal burning power plants is set forth in U.S. Pat. No. 300,593, issued Jun. 17, 1884 which discloses a concrete pavement wherein a small amount of coal ash is combined with other ingredients to form the concrete mixture. However, the coal ash is only present in the mixture in a small amount which translates into a minimal reduction in the slag by-product of the system.
Consequently, there is a pressing need for a process which will utilize coal ash slag discarded as waste from coal gasification processes, and to create a product for which there is a commercial market. Further, with the ever present threat of rising fuel prices and the current abundance of coal, there is a need for a method which will allow coal gasification systems to be more economical and useful as a future fuel producing source.